1. Field of the Invention
The invention relates generally to the field of deposition processes, and more particularly, to systems and methods for an angle limiting deposition mask.
2. Background Information
Many modern flat screen displays with large viewable areas are constructed using a variety of technologies. These include displays such as active-matrix liquid-crystal displays, ferroelectric displays, and electroluminescent displays. During the manufacturing process for these devices, large substrates have to be assembled for use as display screens. Each substrate has hundreds of thousands, often millions, of surface features that form elements such as the individual pixels of the display screen. These surface features have to be coated with different materials, such as metals or polymers, to form the fully functional pixels.
For example, the surface features on a substrate for an electroluminescent display have layers of electroluminescent phosphors coated on them. On conventional active matrix liquid crystal displays, thin films of amorphous or polycrystalline silicon must be deposited onto surface features present on a glass substrate. Active matrix displays are advantageous because they offer improved performance and reduced size (in terms of depth) for specialized applications in laptop computers and high-definition televisions.
A physical vapor deposition process can be used to apply layers of a coating material onto a substrate, and in particular onto the surface features of a substrate. During the physical vapor deposition process, the coating material being applied or a reactant material is evaporated, and the resulting evaporant stream is directed at the surface features of the substrate. The evaporant then deposits onto or reacts with the surface features of the substrate, thereby creating layers of the desired coating material on the surface features.
In some deposition process applications, it is desirable to have coating material deposit onto both a top surface and a side surface of each surface feature on a substrate. Coating material on the top surface of a surface feature can be used for different purposes, including but not limited to use as an electron barrier. Similarly, coating material on the side surface of a surface feature can also be used for a variety of purposes, including but not limited to use as a reflector and as an electron drain. To be useful as a reflector and as an electron drain, the coating material should cover substantially all of the side surface of the surface feature, and should be as close to the surface of the substrate as possible without contacting that surface. Unfortunately, it is not possible to conform to such parameters using known physical vapor deposition equipment and processing techniques. Therefore, tradeoffs must be made that result in the side surfaces not being covered in their entireties, and that create uneven coating material coverage from one side surface to the next.
Accordingly, improved physical vapor deposition techniques that can provide better control over where the coating is deposited are desirable. For example, in some instances the coating is intended to completely cover a side surface of a surface feature, while in other instances control is needed to limit deposition to a top surface of a surface feature, to partially coat a side surface of a surface feature, or even to partially coat a surface of the substrate.
Some of the disadvantages and problems associated with known physical vapor deposition processes have been substantially reduced or eliminated using various embodiments of the present invention.
According to an embodiment of the invention, a method for depositing a material onto a plurality of features located on a surface of a substrate comprises evaporating the material to create an evaporant stream, positioning the substrate so that the evaporant stream strikes the plurality of features over a range of exposure angles between the evaporant stream and the substrate, moving the substrate to vary the range of exposure angles over which the evaporant stream strikes the plurality of features, and moving one or more shutters into the evaporant stream to block any part of the evaporant stream that has an exposure angle greater than a critical exposure angle.
According to another embodiment of the invention, a method for depositing a material onto a plurality of features located on a surface of a substrate comprises evaporating the material to create an evaporant stream, positioning the substrate within the evaporant stream, thereby depositing the material onto portions of the plurality of features, moving the substrate, thereby depositing the material onto further portions of the plurality of features, and moving one or more shutters into the evaporant stream to block any part of the evaporant stream that will contact the surface of the substrate.
According to yet another embodiment of the invention, a system for depositing a material onto a plurality of features located on a surface of a substrate comprises an evaporator configured to evaporate the material to create an evaporant stream, a movable mount configured to hold and move the substrate within the evaporant stream, and one or more shutters positioned to block at least a portion of the evaporant stream from striking the substrate.
An important technical advantage of the present invention includes using a moving shutter to reduce or prevent the deposition of coating material onto areas of a substrate that would be adversely affected by it. During the manufacture of large-screen flat panel televisions for example, this allows substrate elements to be substantially evenly coated with coating material while the surface of the substrate remains substantially free of coating material.